This invention relates to sensing apparatus. More particularly, it is concerned with sensing apparatus for monitoring the passage of objects through a doorway or portal.
In certain situations it is desirable to determine when an object, for example a person, passes through a doorway and the direction of movement through the doorway. Such determination may be useful in systems for passively monitoring activities of persons, particularly elderly persons. One passive monitoring system is described in U.S. Pat. No. 3,885,235. This system monitors the occurrence of certain routine activities and provides appropriate indications in the event that such routine activities do not occur within a preselected period of time.
The passage of persons through a doorway into and out of a room may be monitored to determine the routine activities within a dwelling unit. In particular, it may be desirable to monitor the passage of persons into and out of a bathroom, since a high percentage of home accidents occur within the bathroom. Various types of apparatus have been employed to detect the passage of a person through a doorway, and to determine the direction of movement such that an indication can be provided that a person has entered and/or has vacated a room.